U.S. Pat. No. 3,979,709 to Daniel P. Healey, Jr. 09/07/76 discloses a fuse having a multiply casing of a synthetic-resin-glass-cloth laminate. The casing is produced by the pultrusion process and comprises at least three plies of different materials, namely an outermost ply and an innermost ply both of woven glass cloth and one or more intermediate plies of non-woven glass fiber mat. The above patent describes several such composite materials including more than three plies. One of the advantages of this material as fuse tube material lies in the combination of a high dynamic strength with an unusal degree of flexibility or elasticity. The above flexibility or elasticity is due to the presence of one or more layers of non-woven glass fiber mat with its relatively great interstices between individual fibers. As a result of the great elasticity of pultruded fuse tube materials of the above kind, the above patent suggested a process of affixing fuse caps or ferrules by a rolling and staking process. This way of fastening caps or ferrules to fuse tubes is adequate for many instances but does not involve the maximum of holding force which may be imparted to caps or ferrules mounted on a casing or fuse tube of the kind referred-to above. This problem is solved by the present invention.